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Xref: helios.physics.utoronto.ca alt.security.pgp:11424 alt.answers:2467 news.answers:21451 Newsgroups: alt.security.pgp,alt.answers,news.answers Path: netcom.com!gbe From: gbe@netcom.com (Gary Edstrom) Subject: alt.security.pgp FAQ (Part 1/5) Message-ID: Followup-To: poster Summary: Frequently Asked Questions (FAQ) for alt.security.pgp Keywords: pgp privacy security encryption RSA IDEA MD5 Supersedes: Reply-To: gbe@netcom.com (Gary Edstrom) Organization: Sequoia Software X-Newsreader: TIN [version 1.2 PL1] Date: Mon, 18 Apr 1994 00:50:38 GMT Approved: news-answers-request@mit.edu Expires: Sun, 31 Jul 1994 07:00:00 GMT Lines: 1118 Archive-name: pgp-faq/part1 Version: 9 Last-modified: 1994/4/17 -----BEGIN PGP SIGNED MESSAGE----- Frequently Asked Questions alt.security.pgp Version 9 1994/4/17 ======================================================================== IMPORTANT DISCLAIMER! The use of PGP raises a number of political and legal issues. I AM NOT a lawyer and AM NOT qualified to give any legal opinions. Nothing in this document should be interpreted as legal advice. If you have any legal questions concerning the use of PGP, you should consult an attorney who specializes in patent and/or export law. In any case, the law will vary from country to country. ======================================================================== Beginning with this revision of the FAQ, I have stopped maintaining the master document in Microsoft Word for Windows format. It was just getting to be too much trouble especially since my ultimate output was going to be just a simple ASCII text file anyway. You will no longer see the Word for Windows document in my ftp directory. In place of the Word for Windows master document, you will see the file "pgpfaq.asc" which is a clear signed version of my ASCII master document. You can ftp this file in place of the multi-part version that was posted to usenet if you so desire. This version of the FAQ is being cross posted to news.answers and alt.answers as well as being archived at rtfm.mit.edu. Please check the pgp signatures that I have applied to all parts and versions of this document. Several people reported to me that part 1 of my previous posting of the FAQ had been corrupted. Others, however, said that the file checked out just fine. Please report any signature problem with these files to me. All additions, deletions, or corrections to this FAQ should be directed to me. I will acknowledge all e-mail. Gary Edstrom ftp: ftp.netcom.com:/pub/gbe ======================================================================== Revision History Ver Date Description - --- ---- ----------- 1 09-Dec-93 Proof Reading Copy - Limited Distribution 2 11-Dec-93 First Preliminary Posting 3 19-Dec-93 Second Preliminary Posting 4 01-Jan-94 Third Preliminary Posting 5 15-Jan-94 First Official Posting 6 26-Jan-94 Assorted Changes 12-Feb-94 Changes for version 7: Modified Public Key Server List in section 8.2 Added information on Italian PGP translations in section 1.7 06-Feb-94 Changes for version 8: Fixed a number of minor spelling, grammar, and typographical errors. Removed entry for PGPWinFront 1.2 as it was superceeded by version 2.0. Modified public key server list in section 8. Added additional source for German language pgp files in section 1.7. Added source for Swedish language pgp files in section 1.7. Added information in PGP Integration Project in Appendix I. Changed my ftp address to ftp.netcom.com:/pub/gbe (was netcom.com:/pub...) Added information on ViaCrypt PGP for Unix, WinCIM, & CSNav in section 1.9 Added PGPAmiga-FrontEnd to support products section in appendix I. Added late breaking news from -=Xenon=-. 17-Apr-94 Changes for version 9: Converted file from Word for Windows format to simple text format. Modified the public key server list in section 8. Added Japanese to list of languages for which help files are available. Added information on OzPKE for PGP/OzCIS in Appendix I. Added information on AutoPGP & PGPSORT in Appendix I. Added information on The Ferret BBS in section 1.11. Added information on PGPTalk in Appendix I. Modified answer in 3.3 on extracting multiple keys into a single file. Modified information on HPACK in Appendix I. Added FTP source for StealthPGP. ======================================================================== This FAQ is slanted towards the DOS or Unix users of PGP and many of the examples given may only apply to them. For other systems, I would like to direct your attention to the following documents: MAC: "Here's How to MacPGP!" by Xenon Archimedes PGP comes with its own PGPhints file. Send e-mail to pgpinfo@mantis.co.uk for a list of PGP tips. It should be noted that most of the questions and answers concerning PGP apply equally well to the ViaCrypt(tm) version. Material for this FAQ has come from many different sources. It would be difficult to name each of the contributors individually, but I would like to thank them as a group for their assistance. The files making up this FAQ are available via ftp at ftp.netcom.com:/pub/gbe. The file names are pgpfaq-.asc and are in clearsig pgp format. - -- Gary B. Edstrom | Sequoia Software | PGP fingerprint: Internet: gbe@netcom.com | Programming Services | 2F F6 1B 28 6E A6 09 6C CompuServe: 72677,564 | P.O. Box 9573 | B0 EA 9E 4C C4 C6 7D 46 Fax: 1-818-247-6046 | Glendale, CA 91226 | Key available via finger What is PGP? Subscribe to alt.security.pgp and find out! Late Breaking PGP News From -=Xenon=- - -----BEGIN PGP SIGNED MESSAGE----- Gary, Mac and DOS PGP are now available on MindVox (telnet to phantom.com and login as guest), which is however a pay service BBS. Their modem numbers are: 300/1200/2400-bps +1 212 989-4141 96/14.4/16.8/19.2 +1 212 989-1550 Hayes V.FC 28,800 +1 212 645-8065 My "Here's How to MacPGP!" guide is now available by e-mail with Subject "Bomb me!" to qwerty@netcom.com or by ftp to netcom.com in /pub/qwerty. Please change my address in the FAQ to qwerty@netcom.com. The Guide is also available on the WELL in the Mondo conference, by typing 'texts', but make sure they have updated it to a recent version (2.7). You might also mention steganography finally. I have a list of steganography software in /pub/qwerty as Steganography.software.list, where I have also archived a number of steganography programs. Steganographs let you replace the "noise" of many types of carrier files with an encrypted message. Related to steganography, is the new utility "Stealth", by "Henry Hastur", available by ftp to netcom.com in /pub/qwerty as Stealth1.1.tar.Z for DOS or Unix, or as AmigaStealth1.0.lha. The Amiga version, ported by Peter Simons " will only sign a message, it will not encrypt it. Even though the output looks like it is encrypted, it really isn't. Anybody in the world would be able to recover the original text. ======== 1.2. Why should I encrypt my mail? I'm not doing anything illegal! You should encrypt your e-mail for the same reason that you don't write all of your correspondence on the back of a post card. E-mail is actually far less secure than the postal system. With the post office, you at least put your letter inside an envelope to hide it from casual snooping. Take a look at the header area of any e-mail message that you receive and you will see that it has passed through a number of nodes on its way to you. Every one of these nodes presents the opportunity for snooping. Encryption in no way should imply illegal activity. It is simply intended to keep personal thoughts personal. Xenon puts it like this: Crime? If you are not a politician, research scientist, investor, CEO, lawyer, celebrity, libertarian in a repressive society, investor, or person having too much fun, and you do not send e-mail about your private sex life, financial/political/legal/scientific plans, or gossip then maybe you don't need PGP, but at least realize that privacy has nothing to do with crime and is in fact what keeps the world from falling apart. Besides, PGP is FUN. You never had a secret decoder ring? Boo! -Xenon (Copyright 1993, Xenon) ======== 1.3. What are public keys and private keys? With conventional encryption schemes, keys must be exchanged with everyone you wish to talk to by some other secure method such as face to face meetings, or via a trusted courier. The problem is that you need a secure channel before you can establish a secure channel! With conventional encryption, either the same key is used for both encryption and decryption or it is easy to convert either key to the other. With public key encryption, the encryption and decryption keys are different and it is impossible for anyone to convert one to the other. Therefore, the encryption key can be made public knowledge, and posted in a database somewhere. Anyone wanting to send you a message would obtain your encryption key from this database or some other source and encrypt his message to you. This message can't be decrypted with the encryption key. Therefore nobody other than the intended receiver can decrypt the message. Even the person who encrypted it can not reverse the process. When you receive a message, you use your secret decryption key to decrypt the message. This secret key never leaves your computer. In fact, your secret key is itself encrypted to protect it from anyone snooping around your computer. ======== 1.4. How much does PGP cost? Nothing! (Compare to ViaCrypt PGP at $98!) It should be noted, however, that in the United States, the freeware version of PGP *MAY* be a violation of a patent held by Public Key Partners (PKP). ======== 1.5. Is encryption legal? In much of the civilized world, encryption is either legal, or at least tolerated. However, there are a some countries where such activities could put you in front of a firing squad! Check with the laws in your own country before using PGP or any other encryption product. A couple of the countries where encryption is illegal are Iran and Iraq. ======== 1.6. Is PGP legal? In addition to the comments about encryption listed above, there are a couple of additional issues of importance to those individuals residing in the United States or Canada. First, there is a question as to whether or not PGP falls under ITAR regulations which govern the exporting of cryptographic technology from the United States and Canada. This despite the fact that technical articles on the subject of public key encryption have been available legally worldwide for a number of years. Any competent programmer would have been able to translate those articles into a workable encryption program. There is the possibility that ITAR regulations may be relaxed to allow for encryption technology. ======== 1.7. Where can I get translations of the PGP documentation and/or language.txt files? Spanish: ghost.dsi.unimi.it:/pub/crypt. Author: Armando Ramos German: black.ox.ac.uk:/src/security/pgp_german.txt Author: Marc Aurel <4-tea-2@bong.saar.de> Swedish: black.ox.ac.uk:/src/security/pgp_swedish.txt Italian: ghost.dsi.unimi.it:/pub/crypt/pgp-lang.italian.tar.gz Author: David Vincenzetti Lithuanian: ghost.dsi.unimi.it:/pub/crypt/pgp23ltk.zip nic.funet.fi:/pub/crypt/ghost.dsi.unimi.it/pgp23ltk.zip Author: Zygimantas Cepaitis, Bokera Ltd., Kaunas Lithuania. or Japanese: black.ox.ac.uk/src/security ======== 1.8. Is there an archive site for alt.security.pgp? laszlo@instrlab.kth.se (Laszlo Baranyi) says: "My memory says that ripem.msu.edu stores a backlog of both alt.security.pgp, and sci.crypt. But that site is ONLY open for ftp for those that are inside US." ======== 1.9. Is there a commercial version of PGP available? Yes, by arrangement with the author of PGP, a company called ViaCrypt is marketing a version of PGP that is almost identical to the version currently available on Internet. Each can read or write messages to the other. The list price of ViaCrypt PGP is $98 (US) for a single user license and is NOT available for export from the United States. In addition, it is presently available only for MS-DOS and Unix. Soon to be available are versions for CompuServe's WinCIM & CSNav. Versions for other platforms are under development. While the present product is 100% compatible with free PGP, it is not known if this will remain the case in the future. The address of ViaCrypt is: ViaCrypt David A. Barnhart Product Manager 2104 West Peoria Avenue Phoenix, Arizona 85029 Tel: (602) 944-0773 Fax: (602) 943-2601 E-Mail: 70304.41@compuserve.com E-Mail: wk01965@worldlink.com Credit card orders only. (800)536-2664 (8-5 MST M-F) ======== 1.10. What platforms has PGP been ported to? DOS: 2.3a MAC: 2.3 OS/2: 2.3a Unix: 2.3a (Variations exist for many different systems.) VAX/VMS: 2.3a Atari ST: 2.3a Archimedes: 2.3a subversion 1.18b Commodore Amiga: 2.3a patchlevel 2 ======== From: simons@peti.GUN.de (Peter Simons) Date: Fri, 31 Dec 1993 08:10:53 +0100 Newsgroups: alt.security.pgp Subject: PGPAmiga 2.3a.2 available for FTP TITLE Pretty Good Privacy (PGP) VERSION Version 2.3a patchlevel 2 AUTHOR Amiga port and enhancements by Peter Simons CHANGES This version is re-compiled with SAS/C 6.50. A few minor bugs have been fixed. Additionally, the manual is now available in TexInfo style and can easily be converted into AmigaGuide, postscript, dvi or whatever format. AmigaGuide versions are included. Also for the first time, the alt.security.pgp frequently asked questions (FAQ) are included in the archive. NOTES Please take note that the archive contains a readme file, with checksums for ALL files in the distribution and is signed with my key! Please be careful, if this file is missing or rigged! A mailing list concerning PGPAmiga has been opened on peti.GUN.de. To subscribe, send e-mail to listserv@peti.GUN.de with "ADD your_address PGPAmiga" in the message body. You may add "HELP" in the next line to receive a command overview of ListSERV. SPECIAL REQUIREMENTS none HOST NAME Any Aminet host, i.e. ftp.uni-kl.de ( DIRECTORY /pub/aminet/util/crypt/ FILE NAMES PGPAmi23a_2.lha PGPAmi23a2_src.lha ======== 1.11. Where can I obtain PGP? FTP sites: soda.berkeley.edu /pub/cypherpunks/pgp (DOS, MAC) Verified: 21-Dec-93 ftp.demon.co.uk /pub/amiga/pgp /pub/archimedes /pub/pgp /pub/mac/MacPGP ftp.informatik.tu-muenchen.de ftp.funet.fi ghost.dsi.unimi.it /pub/crypt Verified: 21-Dec-93 ftp.tu-clausthal.de ( wuarchive.wustl.edu /pub/aminet/util/crypt src.doc.ic.ac.uk (Amiga) /aminet /amiga-boing ftp.informatik.tu-muenchen.de /pub/comp/os/os2/crypt/pgp23os2A.zip (OS/2) black.ox.ac.uk ( /src/security (Unix) iswuarchive.wustl.edu pub/aminet/util/crypt (Amiga) csn.org /mpj (see README.MPJ for export restrictions) nic.funet.fi ( van-bc.wimsey.bc.ca ( ftp.uni-kl.de ( qiclab.scn.rain.com ( pc.usl.edu ( leif.thep.lu.se ( goya.dit.upm.es ( tupac-amaru.informatik.rwth-aachen.de ( ftp.etsu.edu ( princeton.edu ( pencil.cs.missouri.edu ( StealthPGP: The Amiga version can be FTP'ed from the Aminet in /pub/aminet/util/crypt/ as StealthPGP1_0.lha. Also, try an archie search for PGP using the command: archie -s pgp23 (DOS Versions) archie -s pgp2.3 (MAC Versions) ftpmail: For those individuals who do not have access to FTP, but do have access to e-mail, you can get FTP files mailed to you. For information on this service, send a message saying "Help" to ftpmail@decwrl.dec.com. You will be sent an instruction sheet on how to use the ftpmail service. BBS sites: Hieroglyphics Vodoo Machine (Colorado) DOS version only (303) 443-2457 Verified: 26-Dec-93 Colorado Catacombs BBS (303) 938-9654 Exec-Net (New York) Host BBS for the ILink net. (914) 667-4567 The Grapvine BBS (Little Rock, Arkansas) Now combined with and known as: The Ferret BBS (North Little Rock, Arkansas) (501) 791-0124 also (501) 791-0125 Carrying RIME, Throbnet, Smartnet, and Usenet Special PGP users account: login name: PGP USER password: PGP This information from: Jim Wenzel ======== 2. General Questions ======== 2.1. Why can't a person using version 2.2 read my version 2.3 message? Try adding "+pkcs_compat=0" to your command line as follows: "pgp - -seat +pkcs_compat=0 " By default, version 2.3 of PGP uses a different header format that is not compatible with earlier versions of PGP. Inserting this option into the command will force PGP to use the older header format. You can also set this option in your config.txt file, but this is not recommended. ======== 2.2. Why does it take so long to encrypt/decrypt messages? This problem can arise when you have placed the entire public key ring from one of the servers into the pubring.pgp file. PGP may have to search through several thousand keys to find the one that it is after. The solution to this dilemma is to maintain 2 public key rings. The first ring, the normal pubring.pgp file, should contain only those individuals that you send messages to quite often. The second key ring can contain ALL of the keys for those occasions when the key you need isn't in your short ring. You will, of course, need to specify the key file name whenever encrypting messages using keys in your secondary key ring. Now, when encrypting or decrypting messages to individuals in your short key ring, the process will be a LOT faster. ======== 2.3. How do I create a secondary key file? First, let's assume that you have all of the mammoth public key ring in your default pubring.pgp file. First, you will need to extract all of your commonly used keys into separate key files using the -kx option. Next, rename pubring.pgp to some other name. For this example, I will use the name pubring.big. Next, add each of the individual key files that you previously created to a new pubring.pgp using the -ka option. You now have your 2 key rings. To encrypt a message to someone in the short default file, use the command "pgp -e ". To encrypt a message to someone in the long ring, use the command "pgp -e c:\pgp\pubring.big". Note that you need to specify the complete path and file name for the secondary key ring. It will not be found if you only specify the file name. ======== 2.4. How does PGP handle multiple addreses? When encrypting a message to multiple addresses, you will notice that the length of the encrypted file only increases by a small amount for each additional address. The reason that the message only grows by a small amount for each additional key is that the body of the message is only encrypted once using a random session key and IDEA. It is only necessary then to encrypt this session key once for each address and place it in the header of the message. Therefore, the total length of a message only increases by the size of a header segment for each additional address. (To avoid a known weakness in RSA when encrypting the same message to multiple recipients, the IDEA session key is padded with different random data each time it is RSA- encrypted.) ======== 2.5. How can I use PGP to create a return receipt for a message? I was planning on including a section on this question. However, while following a similar thread in alt.security.pgp, I realized that there were too many unresolved issues to include an answer here. I may try to include the subject in a future release of the FAQ. ======== 2.6. Where can I obtain scripts to integrate pgp with my email or news reading system? The scripts that come with the source code of PGP are rather out of date. Newer versions of some of the scripts are available via anonymous ftp at ftp.informatik.uni-hamburg.de:/pub/virus/misc/contrib.zip ======== 3. Keys ======== 3.1. Which key size should I use? PGP gives you 4 choices of key size: 384, 512, 1024, or a user selected number of bits. The larger the key, the more secure the RSA portion of the encryption is. The only place where the key size makes a large change in the running time of the program is during key generation. A 1024 bit key can take 8 times longer to generate than a 384 bit key. Fortunately, this is a one time process that doesn't need to be repeated unless you wish to generate another key pair. During encryption, only the RSA portion of the encryption process is affected by key size. The RSA portion is only used for encrypting the session key used by the IDEA. The main body of the message is totally unaffected by the choice of RSA key size. So unless you have a very good reason for doing otherwise, select the 1024 bit key size. Using currently available algorithms for factoring, the 384 bit key is just not far enough out of reach to be a good choice. ======== 3.2. Why does PGP take so long to add new keys to my key ring? The time required to check signatures and add keys to your public key ring tends to grow as the square of the size of your existing public key ring. This can reach extreme proportions. I just recently added the entire 850KB public key ring form one of the key servers to my local public key ring. Even on my 66MHz 486 system, the process took over 10 hours. ======== 3.3. How can I extract multiple keys into a single armored file? A number of people have more than one public key that they would like to make available. One way of doing this is executing the "-kxa" command for each key you wish to extract from the key ring into separate armored files, then appending all the individual files into a single long file with multiple armored blocks. This is not as convenient as having all of your keys in a single armored block. Unfortunately, the present version of PGP does not allow you to do this directly. Fortunately, there is an indirect way to do it. I would like to thank Robert Joop for supplying the following method which is simpler than the method that I had previously given. solution 1: pgp -kxaf uid1 > extract pgp -kxaf uid2 >> extract pgp -kxaf uid3 >> extract Someone who does a `pgp extract` processes the individual keys, one by one. that's inconvinient. solution 2: pgp -kx uid1 extract pgp -kx uid2 extract pgp -kx uid3 extract This puts all three keys into extract.pgp. To get an ascii amored file, call: pgp -a extract.pgp You get an extract.asc. Someone who does a `pgp extract` and has either file processes all three keys simultaneously. A Unix script to perform the extraction with a single command would be as follows: foreach name (name1 name2 name3 ...) pgp -kx $name /tmp/keys.pgp end An equivalent DOS command would be: for %a in (name1 name2 name3 ...) do pgp -kx %a ======== 3.4. I tried encrypting the same message to the same address two different times and got completely different outputs. Why is this? Every time you run pgp, a different session key is generated. This session key is used as the key for IDEA. As a result, the entire header and body of the message changes. You will never see the same output twice, no matter how many times you encrypt the same message to the same address. This adds to the overall security of PGP. ======== 3.5. How do I specify which key to use when an individual has 2 or more public keys and the very same user ID on each, or when 2 different users have the same name? Instead of specifying the user's name in the ID field of the PGP command, you can use the key ID number. The format is 0xNNNNNN where NNNNNN is the user's 6 character key ID number. It should be noted that you don't need to enter the entire ID number, a few consecutive digits from anywhere in the ID should do the trick. Be careful: If you enter "0x123", you will be matching key IDs 0x123937, 0x931237, or 0x912373. Any key ID that contains "123" anywhere in it will produce a match. They don't need to be the starting characters of the key ID. You will recognize that this is the format for entering hex numbers in the C programming language. For example, any of the following commands could be used to encrypt a file to me. pgp -e "Gary Edstrom" pgp -e gbe@netcom.com pgp -e 0x90A9C9 This same method of key identification can be used in the config.txt file in the "MyName" variable to specify exactly which of the keys in the secret key ring should be used for encrypting a message. ======== 3.6. What does the message "Unknown signator, can't be checked" mean? ======== It means that the key used to create that signature does not exist in your database. If at sometime in the future, you happen to add that key to your database, then the signature line will read normally. It is completely harmless to leave these non-checkable signatures in your database. They neither add to nor take away from the validity of the key in question. ======== 3.7. How do I get PGP to display the trust parameters on a key? You can only do this when you run the -kc option by itself on the entire database. The parameters will NOT be shown if you give a specific ID on the command line. The correct command is: "pgp -kc". The command "pgp -kc smith" will NOT show the trust parameters for smith. ======== 4. Security Questions ======== 4.1. How secure is PGP? The big unknown in any encryption scheme based on RSA is whether or not there is an efficient way to factor huge numbers, or if there is some backdoor algorithm that can break the code without solving the factoring problem. Even if no such algorithm exists, it is still believed that RSA is the weakest link in the PGP chain. ======== 4.2. Can't you break PGP by trying all of the possible keys? This is one of the first questions that people ask when they are first introduced to cryptography. They do not understand the size of the problem. For the IDEA encryption scheme, a 128 bit key is required. Any one of the 2^128 possible combinations would be legal as a key, and only that one key would successfully decrypt all message blocks. Let's say that you had developed a special purpose chip that could try a billion keys per second. This is FAR beyond anything that could really be developed today. Let's also say that you could afford to throw a billion such chips at the problem at the same time. It would still require over 10,000,000,000,000 years to try all of the possible 128 bit keys. That is something like a thousand times the age of the known universe! While the speed of computers continues to increase and their cost decrease at a very rapid pace, it will probably never get to the point that IDEA could be broken by the brute force attack. The only type of attack that might succeed is one that tries to solve the problem from a mathematical standpoint by analyzing the transformations that take place between plain text blocks, and their cipher text equivalents. IDEA is still a fairly new algorithm, and work still needs to be done on it as it relates to complexity theory, but so far, it appears that there is no algorithm much better suited to solving an IDEA cipher than the brute force attack, which we have already shown is unworkable. The nonlinear transformation that takes place in IDEA puts it in a class of extremely difficult to solve mathmatical problems. ======== 4.3. How secure is the conventional cryptography (-c) option? Assuming that you are using a good strong random pass phrase, it is actually much stronger than the normal mode of encryption because you have removed RSA which is believed to be the weakest link in the chain. Of course, in this mode, you will need to exchange secret keys ahead of time with each of the recipients using some other secure method of communication, such as an in- person meeting or trusted courier. ======== 4.4. Can the NSA crack RSA? This question has been asked many times. If the NSA were able to crack RSA, you would probably never hear about it from them. The best defense against this is the fact the algorithm for RSA is known worldwide. There are many competent mathematicians and cryptographers outside the NSA and there is much research being done in the field right now. If any of them were to discover a hole in RSA, I'm sure that we would hear about it from them. I think that it would be hard to hide such a discovery. For this reason, when you read messages on USENET saying that "someone told them" that the NSA is able to break pgp, take it with a grain of salt and ask for some documentation on exactly where the information is coming from. ======== 4.5. How secure is the "for your eyes only" option (-m)? It is not secure at all. There are many ways to defeat it. Probably the easiest way is to simply redirect your screen output to a file as follows: pgp [filename] > [diskfile] The -m option was not intended as a fail-safe option to prevent plain text files from being generated, but to serve simply as a warning to the person decrypting the file that he probably shouldn't keep a copy of the plain text on his system. ======== 4.6. What if I forget my pass phrase? In a word: DON'T. If you forget your pass phrase, there is absolutely no way to recover any encrypted files. I use the following technique: I have a backup copy of my secret key ring on floppy, along with a sealed envelope containing the pass phrase. I keep these two items in separate safe locations, neither of which is my home or office. The pass phrase used on this backup copy is different from the one that I normally use on my computer. That way, even if some stumbles onto the hidden pass phrase and can figure out who it belongs to, it still doesn't do them any good, because it is not the one required to unlock the key on my computer. ======== 4.7. Why do you use the term "pass phrase" instead of "password"? This is because most people, when asked to choose a password, select some simple common word. This can be cracked by a program that uses a dictionary to try out passwords on a system. Since most people really don't want to select a truly random password, where the letters and digits are mixed in a nonsense pattern, the term pass phrase is used to urge people to at least use several unrelated words in sequence as the pass phrase. ======== 4.8. If my secret key ring is stolen, can my messages be read? No, not unless they have also stolen your secret pass phrase, or if your pass phrase is susceptible to a brute-force attack. Neither part is useful without the other. You should, however, revoke that key and generate a fresh key pair using a different pass phrase. Before revoking your old key, you might want to add another user ID that states what your new key id is so that others can know of your new address. ======== 4.9. How do I choose a pass phrase? All of the security that is available in PGP can be made absolutely useless if you don't choose a good pass phrase to encrypt your secret key ring. Too many people use their birthday, their telephone number, the name of a loved one, or some easy to guess common word. While there are a number of suggestions for generating good pass phrases, the ultimate in security is obtained when the characters of the pass phrase are chosen completely at random. It may be a little harder to remember, but the added security is worth it. As an absolute minimum pass phrase, I would suggest a random combination of at least 8 letters and digits, with 12 being a better choice. With a 12 character pass phrase made up of the lower case letters a-z plus the digits 0-9, you have about 62 bits of key, which is 6 bits better than the 56 bit DES keys. If you wish, you can mix upper and lower case letters in your pass phrase to cut down the number of characters that are required to achieve the same level of security. I don't do this myself because I hate having to manipulate the shift key while entering a pass phrase. A pass phrase which is composed of ordinary words without punctuation or special characters is susceptible to a dictionary attack. Transposing characters or mis-spelling words makes your pass phrase less vulnerable, but a professional dictionary attack will cater for this sort of thing. ======== 4.10. How do I remember my pass phrase? This can be quite a problem especially if you are like me and have about a dozen different pass phrases that are required in your everyday life. Writing them down someplace so that you can remember them would defeat the whole purpose of pass phrases in the first place. There is really no good way around this. Either remember it, or write it down someplace and risk having it compromised. ======== 4.11. How do I verify that my copy of PGP has not been tampered with? If you do not presently own any copy of PGP, use great care on where you obtain your first copy. What I would suggest is that you get two or more copies from different sources that you feel that you can trust. Compare the copies to see if they are absolutely identical. This won't eliminate the possibility of having a bad copy, but it will greatly reduce the chances. If you already own a trusted version of PGP, it is easy to check the validity of any future version. There is a file called PGPSIG.ASC included with all new releases. It is a stand-alone signature file for the contents of PGP.EXE. The signature file was created by the author of the program. Since nobody except the author has access to his secret key, nobody can tamper with either PGP.EXE or PGPSIG.ASC without it being detected. To check the signature, you MUST be careful that you are executing the OLD version of PGP to check the NEW. If not, the entire check is useless. Let's say that your existing copy of PGP is in subdirectory C:\PGP and your new copy is in C:\NEW. You should execute the following command: \PGP\PGP C:\NEW\PGPSIG.ASC C:\NEW\PGP.EXE This will force your old copy of PGP to be the one that is executed. If you simply changed to the C:\NEW directory and executed the command "PGP PGPSIG.ASC PGP.EXE" you would be using the new version to check itself, and this is an absolutely worthless check. Once you have properly checked the signature of your new copy of PGP, you can copy all of the files to your C:\PGP directory. ======== 4.12. How do I know that there is no trap door in the program? The fact that the entire source code for PGP is available makes it just about impossible for there to be some hidden trap door. The source code has been examined by countless individuals and no such trap door has been found. To make sure that your executable file actually represents the given source code, all you need to do is to re-compile the entire program. I did this with the DOS version 2.3a and the Borland C++ 3.1 compiler and found that the output exactly matched byte for byte the distributed executable file. ======== 4.13. Can I put PGP on a multi-user system like a network or a mainframe? You can, but you should not, because this greatly reduces the security of your secret key/pass phrase. This is because your pass phrase may be passed over the network in the clear where it could be intercepted by network monitoring equipment. Also, while it is being used by PGP on the host system, it could be caught by some Trojan Horse program. Also, even though your secret key ring is encrypted, it would not be good practice to leave it lying around for anyone else to look at. ======== 4.14. Why not use RSA alone rather than a hybrid mix of IDEA, MD5, & RSA? Two reasons: First, the IDEA encryption algorithm used in PGP is actually MUCH stronger than RSA given the same key length. Even with a 1024 bit RSA key, it is believed that IDEA encryption is still stronger, and, since a chain is no stronger than its weakest link, it is believed that RSA is actually the weakest part of the RSA - IDEA approach. Second, RSA encryption is MUCH slower than IDEA. The only purpose of RSA in most public key schemes is for the transfer of session keys to be used in the conventional secret key algorithm, or to encode signatures. ======== 4.15. Aren't all of these security procedures a little paranoid? That all depends on how much your privacy means to you! Even apart from the government, there are many people out there who would just love to read your private mail. And many of these individuals would be -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLbHXFUHZYsvlkKnJAQGFuAQAx9r5I0au9vOehjkjdhAG0ZIYoL3NPjmq Ncipy8KppVsmIMLcILaZh7Lfu9TUwlXH21YUbOVNJwULk4aYhquOplyQo119+BrU n/O8mt77synNziEctSu5vuYA9/NJUmXQZwlP//EJnz/GZ3ZhJeQfLQhsnm2zE1vk ihYJ0RgjIiw= =Hcvw -----END PGP SIGNATURE-----


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